1. Field of the Invention
The invention relates generally to apparatus for detecting malfunctions of even a single electrical device in a whole group of electrical devices, and methods of constructing and utilizing same. More particularly, the present invention relates to a monitoring instrument which is connectable to a group of electrical devices for detecting when one or more of the electrical devices in the group is malfunctioning, and for providing an indication of such malfunction.
2. Description of the Relevant Art
There are known instruments which can be used to detect malfunctions of a single electrical device in a group of electrical devices. For example, U.S. Pat. No. 4,419,621 discloses a "monitoring system for the capacitor batteries of a three-phase filter circuit." The disclosed, patented system is specifically designed to monitor the magnitude and phase of the fundamental frequency components of current flowing from a Y-circuit node by which the individual capacitor batteries are coupled to one another, and to evaluate any variations of the fundamental frequency components to specifically identify defective sectional capacitors.
The patented system has many disadvantages associated therewith. For example, the disclosed system is based on a fairly complex electrical circuit whereby it has a relatively high cost. Further, the patented system does not include its own power supply (or is based on internal current signaling), whereby it cannot be used on many electrical devices, such as metalized-type devices, which do not short out when they malfunction. Also, it would be difficult and impractical to use the disclosed instrument for monitoring a large number of electrical devices because of its complexity.
There are also known instruments, such as disclosed in copending application U.S. Ser. No. 110,115, which can be used to monitor/indicate when a single electrical device has malfunctioned. However, such an instrument is required to be associated with (or monitor) only a single electrical device, so that if a large number of electrical devices were grouped together, such as in a switched bank, then each of the electrical devices would have its own monitoring instrument. Obviously, the use of many monitoring instruments in relation to a large group of electrical devices can be undesirably cumbersome and expensive.
Further, there are known instruments for identifying specific, defective electrical devices which are grouped together with similar electrical devices during normal use. For example, U.S. Pat. No. 4,425,541, 4,536,704 and 4,540,935 disclose several related instruments for identifying defective electric power distribution capacitors. Each of the instruments disclosed in these patents includes a power supply for supplying an alternating current to a de-energized capacitor while the capacitor is still installed in a bank of capacitors and a measurement device for measuring the magnitude of electric current entering the capacitor to thereby determine if it is functioning properly. The disclosed instruments are used by utility company linemen, for example, to accurately determine which specific capacitors (if any) in a bank of capacitors are defective. In use, the linemen must initially disconnect a three-phase capacitor bank from a high voltage line by opening line switches and capacitor fuse protectors, waiting a period of time for the capacitor bank to discharge through internal resistors, and then take a reading of each individual capacitor to determine if it is defective. Such known instruments are quite useful and could, in fact, be used in addition to the present invention. Particularly, the present invention only functions to indicate that there is a malfunction of one or more electrical devices in a group. Once such an indication is made an operator would have to specifically identify/replace which one(s) of the electrical devices are defective, and could do so using the discussed, known instruments. It will be understood, however, that use of the discussed, known instruments is relatively time consuming or labor intensive, whereby use of such known instruments to simply, initially determine if there is a malfunction of any electrical device in a group of the electrical devices can be unnecessarily and undesirably expensive.
Additionally, there are known instruments which monitor both an overload condition and a light-load condition of a single electrical device, such as an induction motor. For example, such an instrument is disclosed in U.S. Pat. No. 4,541,029. As indicated, the disclosed instrument is not intended or constructed for use in monitoring when a single electrical device in a group of electrical devices malfunctions. Moreover, the disclosed instrument is based on a relatively complex circuit and could not be easily or practically adapted for use in monitoring when a single electrical device in a group of electrical devices malfunctions.
Conventional monitoring and testing instruments, including those discussed above, have many problems and disadvantages associated therewith, and have as a whole failed to fulfil a need in the art for a simple monitoring/indicating instrument which can be easily used in association with large groups of electrical devices to provide a simple, initial indication when one or more of the electrical devices in the group has malfunctioned.